Investigations on the macrocysts of different species of the Dictyosteliaceae will be intensified. Special attention will be given to Dictyostelium discoideum following our recent discovery of mating types in this species. We shall attempt (1) to determine conditions governing germination of the macrocysts in order to improve and if possible accelerate the germination process; (2) to determine why some pairs of compatible strains produce abundant cysts, why some produce relatively few, and why others interact positively with either mating types yet produce no cysts when paired; (3) to establish if actual contact between cells of different mating types is necessary to initiate macrocyst formation; and (4) to produce stable mutations (drug resistant, temperature sensitive and morphological) and use these for genetic studies. Continue studies of interspecific mixtures to determine why one species inhibits the growth and/or normal development of another. Continue investigations on the more primitive cellular slime molds (e.g., Guttulinopsis and Copromyxa) wherein myxamobae aggregate and form multicellular fructifications that show no demarcation into supportive stalks and spores. Attempt to identify the putative gaseous substance produced in laboratory cultures of the Myxobacterium Chondromyces that limits or precludes normal fructification.